Solvent recovery processes which operate on the basis of distillation of the soiled solvent and condensation of the distilled vapor are well known. For separating mixtures of solvents from one another, fractional distillation is commonly effected in a single stage or a multi-stage process, depending upon the degree of purity required of the recovered solvents. In dry cleaning apparatus, it is known to pass the soiled solvent through a filter and into a still and to condense the boiled off solvent vapor, the condensate being fed back into the dry cleaning treatment chamber. In industrial dry cleaing apparatus, a greater or lesser degree of control of processing temperatures is effected, dependent upon the nature of the solvent or solvents being processed and the scale of the plant.
Although the prior art solvent recovery techniques have been efficient in their recovery of solvents, they have been wasteful in their utilization of energy. At best, only the simplest of heat exchange arrangements for pre-heating liquid inputs to the prior art stills has been known. With the recently awakening consciousness of energy conservation needs, coupled with increasing energy consumption costs, the need has arisen to operate in the field of solvent recovery with increased efficiency in energy utilization.